Nanoparticle blood test detects amoxicillin allergy that standard test missed

Researchers at the University of Malaga have built a blood test that they say diagnoses allergy to amoxicillin and other penicillin-type antibiotics more accurately than the standard commercial test. The findings were published in the journal Materials Today Bio, with Yolanda Vida and María I. Montañez of the university's Department of Organic Chemistry as lead authors. The study also involved researchers from the IBIMA BIONAD Platform, the Inflammatory Diseases Network, and the Regional University Hospital of Malaga.

The team tested blood samples from close to one hundred people: 50 patients with confirmed amoxicillin allergy and 44 who tolerated the antibiotics without problems. When they compared their platform against ImmunoCAP, the most widely used commercial allergy test, and against a conventional method called RAST, the new platform detected allergy to amoxicillin specifically with 98% sensitivity. ImmunoCAP, tested on the same samples, detected only around 17%. Sensitivity here means the share of true allergy cases the test correctly flags, so a large gap in that number means many real allergies were going unrecognized by the existing commercial test.

The new test relies on nanoparticles about 30 nanometers across, small enough that thousands could fit across the width of a human hair. Each particle has an iron oxide core, which makes it magnetic, wrapped in a shell of silica. Ezequiel Pérez-Inestrosa, Professor of Organic Chemistry at the University of Malaga and one of the study's authors, describes the particles as acting "like a tiny magnet covered with thousands of molecular hooks."

Those molecular hooks are built to grab a specific antibody called IgE, the immune molecule responsible for the allergic reaction, if it is present in a patient's blood. Because the particles are magnetic, they can be pulled out of a blood sample directly rather than separated using lengthy centrifugation, the spinning process conventional tests rely on to isolate components of a sample. María José Torres, Professor of Medicine and another of the study's lead researchers, says that in the tests performed, the system captured nearly all true allergy cases while cutting down both false negatives and false positives. Avoiding the standard drug provocation test, in which a patient is given the suspect antibiotic directly to see if a reaction occurs, is also a goal of this method, since that test carries real risk to the patient.

Penicillin allergy is reported far more often than it is real. Pérez-Inestrosa notes that between 8% and 25% of the population report being allergic to penicillins, but only between 1% and 10% actually are. A separate review of beta-lactam allergies, the broader antibiotic family that includes penicillins, cephalosporins, carbapenems and monobactams, cites a similar pattern: 10% to 12% of the population, particularly women, report allergy to penicillins, yet between 70% and 90% of those who claim to be allergic have not actually experienced a hypersensitivity reaction.

A retrospective study of 300 hospitalized adults in South India found that over 50% of patients labeled as allergic to penicillin, and 21% of those labeled allergic to cephalosporin, were classified as low risk for true allergy using standardized scoring tools. Among patients in that study who were given alternative, non-beta-lactam antibiotics because of their allergy label, 44% were in that low-risk group and might have safely received the drug they were said to be allergic to instead. The consequences of an incorrect allergy label are consistent across sources: patients are steered toward substitute antibiotics that are generally less effective, more toxic, and linked to bacterial resistance, C. difficile infections, longer hospital stays, and higher costs.

The Malaga team is direct about the limits of what a study of fewer than 100 people can establish. The authors state that further, larger studies across multiple hospital centers and formal clinical validation are needed before the nanoparticle platform can be introduced into hospitals and used routinely. The comparison so far covers amoxicillin allergy against two existing tests, ImmunoCAP and RAST, in one dataset; how the platform performs on other penicillins, or in more diverse populations, is not yet reported.

Other groups are approaching the overdiagnosis problem differently, without relying on new nanoparticle chemistry. Tools such as the PEN-FAST score, a point-based risk calculator built from a patient's allergy history, and a related tool for cephalosporin allergy called CEPH-FAST, are already used at the bedside to flag patients who could safely undergo a direct oral challenge instead of being treated as allergic by default. A review of beta-lactam allergy management similarly stresses that patient history, skin tests, and provocation tests remain the established diagnostic tools, and that substituting a beta-lactam with an alternative antibiotic is not always the safest option even when an allergy is suspected. Whether a nanoparticle-based blood test would replace, or work alongside, these existing history-based and challenge-based approaches is not addressed by the Malaga study.